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Tag Archives: ball screws in linear motion
All Your Equations In One Place
When a linear motion solution is in place & running, it’s easy for the casual observer to think it looks easy. That’s what our industry is all about; making the difficult or even impossible look easy.
But what few people outside the industry realize is just how much work needs to go into the design of a successful linear motion system. The old adage “Measure twice, cut once” doesn’t even begin to cover all the variables, that have to be dealt with.
Now, a new app looks to make that successful design at least a little easier. The Design Guide Pro not only offers selectors for Bevel Gears, Worm Gear Jacks, Bearings and Electric Cylinders, but it also has a calculator section. Here, you’ll find tools to help you establish Energy, Critical Speed, Column Load, Torque and Nut Life as well as helping with Unit Conversions.
All in the palm of your hand. Check it out today by clicking here.
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Loading a Standard Ball Nut
Check out these videos on how to load a standard ball nut:
When the arbor will not slide over the machined journal
When the arbor will slide over the machined journal
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4 Reasons Why Your Ball Screw Assembly May Fail
Premature failure may be caused by any of the following:
- Misalignment of the ball nut to the screw which results in side loading or eccentric loading will reduce life. Additionally, this may cause the ball bearings to split or get flats on them. The ball bearings may even break out of the return tubes.
- Metal chips, dirt or debris in the ball nut may impede the call bearings from free circulation. The ball bearings may get flats on them because of skidding,
- Lack of lubrication. Proper lubrication will help dissipate heat and reduce metal-to-metal wear of components.
- Exceeding the ball nut critical speed can break pickup fingers off, causing the balls to come out of the nut. Exceeding the screw critical speed will cause the whip resulting in misalignment.
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Integral Safety Threads
Ball nuts can fail for a variety of reasons. Primarily, it’s fatigue of the bearing balls or the threaded surface, which is why proper lubrication (link to lube blog post) is so important. However, ball nuts can fail prematurely due to misalignment, impact loading, contamination, or external damage to the return circuits. Premature failure may result in the loss of some or all of the balls between the nut and screw. When all the balls are lost the nut is no longer engaged with the screw and therefore may not move when the screw is rotated or, in vertical applications, will free fall along the screw.
In applications where this loss of ball type failure could result in injury or death, this failure needs to be considered in the design. Possible preventative measures include the use of two or more screws supporting the load, use of nuts with multiple independent ball recirculation circuits, use of Ball Deflectors which prevent the balls from exiting the ball nut out the ends.
There is one more preventative measure that has proven itself in testing and in practical use; Integral Safety Threads. These unique solutions that provide the ball nut with a secondary safety thread – a reverse thread in the nut body itself. This special thread extends from the ID (Internal Diameter) of the nut to below the OD (Outside Diameter) of the screw without making contact. In the unlikely event that all the balls in the nut are lost, this “safety” thread will engage the screw and prevent free-fall. Although this thread can be used to lower the load to a safe position, it is not to be used otherwise. This can also be accomplished with the use of a special flange if the ball nut body cannot accommodate the Safety Thread feature.
